The step load response of an internal combustion (IC) engine in transient after a load impact is a feature mostly influenced by the engine displacement, the hardware of the engine (e.g., whether it has a standard turbocharger, a turbocharger with waste gate or variable geometry, etc.), and by the software strategy for driving the air and fuel actuators (e.g., exhaust gas recirculation, turbocharger with variable geometry turbine (VGT), fuel injector configuration, etc.) with respect to the requirements of emissions legislation (e.g., visible smoke, NOx, etc.), noise or vibrations.
Engine systems as a whole react in a linear manner during the application of a transient external load. Initially, the load is applied to the drive shaft of the IC engine. The IC engine speed decreases when the load increases. The engine speed drop is influenced by whether the governor is isochronous or has a speed drop. The air flow is increased to provide additional air to the IC engine by modifying the air actuators. A time delay is necessary to achieve the new air flow set point. The fuel injection quantity, which is nearly immediate, is increased with respect to both the smoke limit and maximum allowable fuel quantity. The engine then recovers to the engine speed set point. The parameters associated with an engine step load response in transient after a load impact are the speed drop and the time to recover to the engine set point.
With conventional IC engine systems, a fuel injection system under the control of an electronic control module (ECM) provides fuel to the combustion cylinders. The maximum mechanical torque output from the engine is a limiting factor on the normal maximum fuel level which is provided to the combustion cylinders. Under a high external transient load as described above, the fuel level remains limited to the normal maximum fuel level supplied to the combustion cylinders, and the engine speed drop and recovery time can be excessive.
What is needed in the art is a power boost method for an IC engine which improves engine speed drop and recovery time.